CA1216942A - Multistate optical switching and memory using an amphoteric organic charge transfer material - Google Patents

Abstract

ABSTRACT

A multistate organic optical storage medium is disclosed, wherein an optical beam can switch any "data storage spot" on said optical storage medium into three or more memory states.
The optical storage medium may consist of a mixture of bistate switching modules, or it may consist of large delocalized amphoteric molecules. The illuminated area of said optical storage medium will undergo an electrochemical topactic redox reaction which will cause certain moieties in the illuminated area to change oxidation state. By changing the intensity of the optical "write" beam the illuminated area can be switched to a plurality of specific states each state having a unique set of oxidation species. An optical/spectroscopic means is used to identify the presence of oxidation species and to "read" the data stored.

Description

BACKGROUND AND/OR ENVIR_ MENT OF T~ INVENTION
1. Field of the Invention The present invention pertains generally to the use of a mix~ure of several charge transfer compounds of varying redox potential or the use of a single amphoteric organic charge transfer compound to produce optical devices and more particularly ~o the use of the.se organic charge transfer materials as a memory medium and switching mechanism for an optical system.

2. Descri~tion of the Contemporary and/or Prior Art With the advent of the inforrnation revolution, recen$
research activi~ie~ have focused on developing optical storage systems and optoelectronic switches. ~he interaction of laser light with matter has been intensely investigated because of its use in optical memory systems. Potentially, optical recording can produce information storage densities in excess of 100 million bi~s per square centimeter. Currently many optical memory devices rely on crystalline phase tran~itions (J. Stuke, Journal of Non-Crystalline Solids, Vol. 4, (1970)~ or on photochemical hole burning (PHB) in which a laser pits the material in an effort to store data. An article entitled ~Laser Marking of a Thin Organic Film" by J.J.Wrobel et al, Applied P~ysics Letter 40, (11) 1 June 1982, describe~ such a technique using a laser beam to burn holes in a thin organic film. Similarly, optical writing on blue sputtered iridium oxide films i~ reported by Mabosch et al in Ap~lied Physics Letter 41 (1), 1 July 1982. This technique uses an optical writing mechanism to thermally induce dehydration at temperatures below the melting point of the optical medium. An article entitled aLight-induced Phenomena in ~ye-polymer Systems~ by V. Novotny et al, The Journal of Ap~ d P~ysics 50

(3), March 1979, describes an optical markiny process based on diffusion in a dye-polymer system.
The prior art optical storage systems have one overriding disadvantage - prior art optical medium is not erasable. As a result, optical storage technology has found little application in computer technology, which requires both read, write and erase functions.

~.S. patent 4,371,883 (entitled ~Current Controlled Bistate Electrical Organic Thin Filrn Switching Device (TCNQ)~, filed March 14, 1980) discloses a class of organic charge transfer salts, such as CuTCNQ, which exhibit stable and reproducible bistate ~witching between an equilibrium, or first ~tate, and a second Rtate, in the presence of an applied electrical field. These reference~ di~close that certain organic charge transfer salts will undergo a bi~tate reversible electrochemical topotactic redox reaction in the presence of an applied electric field. The electrical field causes the organic salt to switch from a first state to a second (i.~., bistate switching). A detectable impedance change occurs between the equilibrium, or first state, and the second state thereby allowing one to determine if a particular area is in the first or second state. In ~peciic, an electrical field is applied across a thin film of CuTCNQ, or an equivalent organic charge transfer salt. When the applied electrical field exceeds a threshold value ~he impedance across the thin organic film will drop from a relatively high impedance to a relatively low impedance.
Two papers written by Richard S. Potember et al report that when the organic film is electrically switched, the fiecond state has different optical properties from the equilibrium or first state~ The Vibrational and X-ray Photoelectron Spectra of Semiconducting Copper-TCNQ Films~ Chemica S ripta, Vol. 17, 219-221 (1981); and (2) ~Electrical Switching and Memory Phenomena in Semiconducting Org~nic Thin Films~ America Chemical Society Sym~osium Series No. 184 (1982). These ar~icles describe infrared spectroscopic means and reference well known Raman spectroscopic techniques (S. Matsuzaki et al, ~Raman Spectra of Conducting TCNQ Salts" Solid State Communica-tions, Vol. 33, pp. 403-405, 1980) for determining if the CuTCNQ
film, switched by an AC or DC electric field is in the first or second state. ~ollow-up work reported by E. I. Kamitsos et al used Raman spectroscopic techniques to verify the electrochemical charge transfer equation described in the above-referenced articles which causes the CuTCNQ salt to switch from the first to second state: aRaman Study of the Mechanism of Electrical Switching in CuTCNQ films~ Solid State Communica-tions, Vol. 42, No. 8, pp. 561-565 (1982). ~he3e papers point ou~ ~hat spectroscopic means can be used to di~cern whether an area of CuTCNQ switched by an applied electrical field i~ in ~he first or second state.
Potem~er and Poehler, the present inventors, with Benson, - filed a Canadian patent application entitled ~Optical Storage and Switching Device~ ~sing Organic Charge Transfer Salts~, Serial No. 450,479, filed March 26, 1984, which is directed to a bistate optical switching device. They discovered that certain organic charge transfer salts will also experience two-state switching when exposed to optical radiation. It was discovered that when the optical radiation exceeds a certain threshold, the organic charge transfer salt switched from a first to a second state. Spectroscopic and other optical means are used to determine if a portion of the organic charge transfer material was in the first, equilibrium, or second switch state. That pending ~.S. application describes certain optical devices used to store binary information -- the first state can be represented by a 50~, and the second or switched state can be represented by a "l". That application also describes certain optical and thermal means for switching the organic material from the switched state ("l" state) back to the equilibrium state (~0~ state). ~owever, the organic optical devices described in that pending application are two-state ~ystems which can only 6tore two bit~ of information on a particular area of the organic optical ~torage medium.

SUMMARY 0~ THE INVENTION

The present inventors have improved the organic charge transfer switching system described in Canadian patent , .. , .. ~
application Serial No. 4S0,479, and have developed an organic storage medium which can optically store three or more bits of information at the same spot on the storage medium. The inventors have discovered that 60me amphoteric organic charge transfer materials can undergo ~ electron transfer reactions which enable the optical ~torage material to be ~witched among a ~ of states. The inventor~ have further di~covered that ach state can be uniquely identified by spectroscopic means and that energy from optical, infrared or thermal sources can be used to era e the storagP medium and return it to its first or base ~tate.
The invented apparatus comprises: (1) an optical storage medium, generally in the form of a film of either a mixture of several charye transfer compounds of varying redox potential or of a single amphoteric organic charge transfer compound which is capable of undergoing a multistage charge transfer reaction; and (2) a source of applied optical energy which illuminates a spot on ~he optical st~rage medium and causes that spot to switch to one of a plurality of states. The organic material will switch from one state to another state as the applied optical field strength is increased.
The inventors have discovered that at particular optical field strength~, the amphoteric medium will ~witch into a particular state~ The inventors have also digcovered that each state of ~aid multistage electron transfer reaction, can be identified by the presence of a unique set of redox species Changes in the electronic or fundamental absorption modes are used to ~read~ the state of a ~data ~torage 8pot~ (i Oe- ~ each spot to be illuminated by the optical beam) on the optical storage medium by identifying the particular set of redox species present.
For example, with an amphoteric organic charge transfer material having a 4-stage electron transfer reaction, an optical ~write~ beam can be used to ~witch the optical ~toraqe medium from the base state to one o three states, depending on ~he intensity of the optical field ~trength. Therefore, the optical ~write~ beam could be used to ~tore multiple bits of data at each ~data gtorage spotn~ Similarlyl optical and spectroscopic means can ~read~ the multiple bits o data ~tored at any ~data storage spot~ on the film. By appropriately placing the ~data storage spotsW on the optical storage medium, a conventional two dimensional configuration can be used to make an extremely dense optical storage device.
The inventors also discovered that thermal energy (generated by an optical or thermal means) can be used to "erase" all or part of the optical storage film and return each state of the multiple storage spot to its ~ase or equilibrium state. The reverse multistage charge transfer reaction is a thermally activated process. It was also di~covered that diffexent organic charge transfer materials can be selected to produce either threshold or memory optical switching.
The new optical storage medium generally consists of a thin film of an amphoteric organic charge transfer material.
The amphoteric organic charqe transfer material is capable of undergoing a multistage charge transfer reaction. Each stage of said charge transfer reaction electrochemically generates multiple redox species. Each stage or state ~an be identified by observing the unique set of redox species generated. The amphoteric organic charge transfer material can be fabricated in several ways, which will be de~cribed in detail later in this specification ~irst, an amphoteric mixture can be produced by growing thin films containing a mixture o~ two different radical ion salt~. Each radical ion salt, such as CuTCNQ or CuTCNQ(i-Pr)2, exhibits~eparate bistate switching reactions.
Secondly, an amphoteric molecule can be complexed by chemically linking various acceptor molecules (such as TCNQ, TNAP, or TCNQIi-Pr)2 together through ~igma and pi bonding systems.
Third, highly delocalized radical ion acceptor molecules can be synthesized which exhibit the optical switching and amphoteric properties.
Accordingly, it is one object of the pre~ent disclosure to provide an optical medium which can be optically switched from an equilibrium state to two or more switched states ~redox states). ~he level of the electromagnetic field at optical frequencies determines into which ~tate the optical medium is switched. Further, the particular switched state can be subsequently identified by observing the changes in the electronic optical spectrum or the change in the fundamental absorp~ion modes.
The second object of the present disclosure is to produce an amphoteric orgar,ic charge medium which undergoes a multistage charge transfer reaction when subjected to an applied electric field. Electromagnetic energy at optical frequencies causes the material to undergo successive stages of a redox reaction as the optical field strength is increa6ed. This stepwise switching allows an optical beam to switch the amphoteric organic charge transfer material from one stable oxidation state to a 6econd, third, or fourth stable state. Each state can be identified by observing the optical characteristics of the redox ~pecies associated with ~hat particular switched state. The amphoteric organic charge transfer material is Uerasable~ by applying thermal energy, which rever~es the reaction and returns the material to i~s equilibrium state. Different amphoteric organic charge transfer materials can be selected to provide either memory or threshold multistate switching.
A third object of the present disclosure is to use the amphoteric charge transfer material to produce a multistate optical storage device. An optical "write~ beam is controlled to illuminate at least one ~data ~torage ~pot~ on ~he amphoteric film. The level of the applied electromagnetic field of the optical "writeR beam is adjusted so that the illuminated ~data storage spot~ can be switched to a particular one of a plurality of sta~es. Data from a ~cata storage spot~ can be subse~uently ~read~ by determining the optical characteristics of that ~data storage spot" through ~pectroscopic techniques. The stored data can be "erased~ by applying thermal energy to a particular part of the amphoteric organic charge transfer film, thereby returning that portion of the film to its base or equilibrium state.
While several features of the present disclosure relate to optical storage medium and op~ical memory devices, it is to be understood that the above--mentioned multistate switching function of the amphoteric organic charge transfer material can have application in other optical devices and optically sensitive appaxatus.

BRIEF DESCRIPTION OF THE DRAWI~GS
. _ Drawings which illustrate embodiments of the invention;

Figure 1 is a graph of the Raman spectral bands for bistate CuTCNQ; ~igure la ~hows the spectral bands for neutral TCNQ;
Figure lb shows the spectral bands for CuTCNQ in the first state; Figure lc shows the spectral bands for CuTCNQ in the switched state;
Figure 2 is a Raman spectrophotometric plot illustrating each of the three switched states of Cu[TCNQ (i-Pr)2~; Figure 2a shows the optical characteristic6 of the base state; Figure 2b shows the optical characteristics of the second state; Figure 2c shows the optical characteristics of the third state;
Figure 3 is a ~able showing the relationship between reduction potential of the acceptor moiety and the field strength switching threshold;
Figure 4 is a table which outlines some of the observed visible color changes in bistate material which can be mixed to form multistate material;
Figure 5 is a qraph showing the fluorescence of TCNQ[~OMe)(O-i-pr)] in its neutral state;
Figure 6 shows molecular drawings of radical ion acceptor molecules which can be used to make multistate switching material in accordance with the present disclosure;
Figure 7 shows several examples of two chemically linked radical ion acceptor molecules which exhibit multistate optical switching;

Figure 8 shows several highly delocalized radical ion acceptor molecules which exhibit multistate switching as taught by the present disclosure;

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Figure 9 ~how~ ~everal highly deloc~lized r~dical ion donor molecules ~hich exhibit multistate ~witching as taught by the present disclosure;
Figure 10 graphically illu6trates the generalized optical ~witchinq characteri~tics of the multistate amphoteric charge transfer materi~ t~ught by the present disclosure;
Figure 11 i8 a truth table illu~tr~ting the generalized optical ~witching characteri~tic~ of multi~tate ~mphoteric charge transfer material aR taught by the pre6ent disclo~ure;
~igure 12 ~s a schematic diagram of an optical storage 6ystem u~ing such multi6tate amp~oteric charge tran6fer material as taught by the pre6ent disclosure;
Figure 13 is a schema~ic repre~entation of the optical ~ean~
used to evaluate the 6tate of each ~data ~torage spot~; and, Figure 14 i~ a 6chematic drawing 6howing the thermal erasure means.
DETAILED DESCRIPTION 0~ THE PREFERRED EMBODIMENT

. _ To understand multi6tage 6witching it i8 necessary to understand 60me of the principles of bistate optical fiwitching as described in the Canadian application entitled ~Optical Storage and Switching Devices using Optical Charge Tran6fer Salt~ (SN 450,47~. The basic electrochemical topotactic redox reaction which occur~ when a bistable organic charge tran~fer alt, Ruch ~s CuTCNQ, i6 illuminated with a beam having sufficient optical field strength and switched from a fir~t to a second 6tate, i~
chown below:

optica1 Pnersy (1) [M tTcNQ )]n ~~~'Mx + [M (TCNQ )]n-x + (TCNQ) x Fir6t state Second state It is believed that switching occur6 because the optical beam (i.e., an electromagnetic field ~t optical frequencies) ,f cau~es the bonds between the organic electron acceptor (in this case TCNQ) and the donor (repxesented b~ M) to break, allowing a chaxge to transfer from the donor ~o the organic electron acceptor. The foxegoing Equation (1) clearly shows a change in charge distribution as the organic salt switches from a first to a ~econd state. In the first, or ba~e Rtate, the organic electron acceptor moiety i8 found almost exclusively in the reduced form (TCNQ ). However, in ~he second, or ~witched state, the organic electron acceptor ~oiety is found in both its reduced (TCNQ-) and neutral ~TCNQ) forms.
It will be notad from Equation ~1) that each state is associated with a unique ~et of redox specie~. In the first state the acceptor moiety i6 found almoRt exclusiv~ly in the reduced form (e.gO ~ only the TCNQ~ ~pecies is present~;
whereas, in the switched, ox second tate, the acceptor moiety exists in both the reduced and neutral form (e.g., TCNQ~ and TCNQ redox species are present). ~isual, 3pectroscopic, fluorescent and/or other optical means can be ued to determine whether the bistate charge transfer salt i~ in the fir~t or second state by identifying optical characteristics associated with each redox species. Figure 1 shows the Raman spectral bands for the organic charge transfer ~alt CuTCNQ: Figure 1a ~hows the spectral bands for neutral TCNQ (e.g., TCNQ); Figure lb shows the spectral bands for CuTCNQ in the first state where essentially all the organic electron acceptor moiety is in a reduced form (e.g., only the TCNQ redox species is present); Figure lc shows the ~pectral band for CuTCNQ in the - sL~v, tcke~
second, or ~ state, where the organic electron acceptor moiety is in both the reduced and neutral oxidation ~tates (e.g., both the TCNQ- and TCNQ species are present). The Raman spectral bands are fundamental absorption mode~ which are sensitive ~o the oxidation state of the organic electron Z

acceptor moiety, thereby uniquely identifying the redox ~pecies present (i.e., in our example, determining if the TCNQ or TCNQ
redox species are present). When CuTCNQ ifi used as the organic charge transfer ~alt one need only analyze the 1451 cm 1 spectral band to determine if the organic salt is in the first .. ... . ..
or ~econd ~tate. If the CuTCNQ organic charge transfer salt is in the first state, the spectral intensity is low at 1451 cm l; if the organic charge transfer salt is in the Recond state, the spectral intensity is high a~ 1451 cm l.

10 FABRICATING M~LTISTATE_AMPHOTERIC CHARGE TRANSFER MATERIAL
FROM TWO OR MORE BISTATE ORGANIC CHARGE_TRANSFER_SALTS
The first method of fabricating a multistate amphoteric charge transfcr material, as taught herein, is to produce a polycry~taline mixture from two biRtate organic charge transfer salts. Under this method a film is grown containing two different radical ion salts mixed in a predetermined ratio. For exam~le, neutral TCNQ and neutral TCNQ(i-Pr)2 are added to a solvent such as CH3CN to form a solution. The solution is allowed to interact with a copper metal foil and corresponding complexes of Cu2[TCNQ:TCNQ(i-Pr)2] are grown on the metal 'oil producing a polycrystalline film. (It is to be understood that it is also within the contemplation of the invention to ~se other known methods to produce the polycrysta~ine mixture).
When Cu2[TCNQ:TCNQ(i-Pr)2], an a~photeric charge transfer material, is irradiated by an optical source (such as an Argon ion laser) the optical characteristics of the material change with increases in the optical power density (watts/cm ). Three different optical spectra were observed which correspond to three switched states. Three switched states were noted because the optical field strength required to switch CuTCNQ from its base state to its fiecond state is higher ~z~
than the optical energy nece~3sa~y to ~witch CuTCNQ(i-Pr)2.
The Ap~licants were able to use such field strength dependence to stepwise switch each copper bistable salt from its base state to its switch state at a different optical field strengths.
Figure 2 is a Raman spectrophotometric plot illustratinq each of the three ~tates of Cu[TCNQ: TCNQ(i-Pr~2]. Figure 2a shows the optical characteristics of the unswitched or base ~tate. In the base ~tate, strong v4(C= C ~tretching) Raman bands 10 were obser~ed fox both copper ~CNQ and copper TCNQ(i-Pr)~. The copper TCNQ(i-pr)2 stretching frequency is at 1390 cm 1 which is ~hifted approximately 15 cm 1 from the copper TCNQ stretching band at 1375 cm 1. The Raman bands 10 identify the presence of the TCNQ and TCNQ (i-Pr)2 moieties in their reduced states ( i . e., the TC~Q~ and TCNQ(i-Pr)2~
redox species are present). Figure 2b shows the optical characteristics of the second state, which can be identified by the appearance of the Raman band 12 at 1451 cm 1 which is associated with the presence of the neutral TCNQ(i-Pr)2 redox species. To switch from the base ~tate (illustrated in Figure 2a) to the second state (illustrated in Figure 2b) an optical field strength had been applied to the film which was ~uf f icient to switch the TCNQ ( i-Pr ) 2 from its reduced species to its neutral species. ~owever, the optical ~ield strength was no~ sufficient to switch the TCNQ molecules. The second state can be identified by the presence of a new apectral peak at 1451 cm 1 (element 12, Fig. 2b) corresponding to neutral TCNQ(i-Pr)2 species and a decrease in the intensity of fully charged TCNQti-Pr)2S ~pecies at 1462 cm 1.
Figure 2c shows the film after the optical field intensity had been increased to a higher threshold level. The second optical field intensity now exceeds the threshold necessary to induce bistate switching in both CuTCNQ and CuTCNQ(i-Pr)2 ~altfi. The re8ult~ng electrochemic~l charge transfer re~ction now cau~e6 some of the CuTCI~IQ charge transfer complex to ~witch producing ~he neutral TCNQ redox specie. The op~ical characteri6tic~ of the third state can be identified by the sppearance of Raman band 14 at 1451 cm 1 which is a6sociated with the present of the neutral TCNQ redox specie~.
The multi~tate ~witching ob~erved in Cu2 l~CNQ:TCNQ~ i-Pr~ 2] mlg~t be~t be under~tood in view of Equations 2-~ following:

10~2) Cu TC~iQ (i~Pr) 2 -- CU ~ TCNQ (i-Pr) 2 ~ Cu~TCNQ (i-Pr ) 2 (3) Cu TCNQT ~ Cu + TCNQ ~ Cu TCNQ~

(4) n [Cu2t(TCNQ~)(TCNQ(i-Pr)2)]
(State A) x[Cu] ~ x¦TCNQ(i-Pr)] + n-xlCu TCNQ~i-Pr)2~ ~ n[Cu (TCNQ~)]
(State B) _ (x+y)Cu + x[TCNQ(i-Pr)2] ~ y[TCNQ~

n-x[Cu (TCNQ (i-Pr) 2] + n-y [Cu+ (TCNQ~)]
(State C) where~ E2 ' El Equation 2 describe~ the two ~tate switching xeaction of a Cu~CNQ(i-Pr~2 film when an optical beam having an intensity exceeding El illuminates the ilm. In this electrochemical ~eaction the switched state can be uniquely identified by detecting the presence of both the TCNQ(i-Pr)2 and 1~

TCNQ(i-Pr)2T redox ~pecie6. Equation 3 shows the two state switching reaction of a CuTCNQ film when an optical beam having an intensity exceeding E2 illuminates the film. In this electrochemical reaction, the switched state can be identified by the presence of both TCNQ and TCNQ redox species. It will be noted that the switching optical threshold level for the two Equations i5 dependent upon the redox potential of the acceptor~moiety. The table in Figure 3 shows the relationship between reduction potential of the acceptor moiety and the field ~trength switching threshold. In our example, a multistate amphoteric material can be fabricate~ from copper TCNQ and TCNQ(i-Pr)2 because the optical threshold to switch CuTCNQ is different from the optical thre~hold necessary to ~witch CuTCNQIi-Pr)2. In general, ~uch field strength dependence can be used to stepwise swi~ch each bistable charge transfer salt thereby allowing the fabrication ~f a multistate amphoteric charge transfer medium.
Equation 4 shows the switching characteristic of the amphoteric mixture Cu2[TCNQ:TCNQti-Pr)2]. It will be noted that the amphoteric film is switched to the second state (state B) after the film has been illuminated with an optical field intensity greater than E1 but less than E2. The ~econd state (state B) can be identified by detecting the TCNQ(i-Pr)2 redox species. As previously shown in Figure 2b, the optical characteristics of the TCNQ(i-pr~2 redox species can be identified by the Raman spectral band 12. When the optical intensity equals or exceeds E2 the amphoteric material will be switched into the third state (state C~. The third state is identified by detecting both the TCNQ and the TCNQ(i-Pr)2 redox species. Such redox species can be detected by Raman spectroscopic means as shown in Figur~ 2c.

Therefore, Cu2[TCNQ:TCNQ~i-Pr)2] can be switched into three 6tate6: first, the amphoteric material will remain in the ba~e ~tate [~tate A) if the optical intensity is le s than E1;
secondly, the amphoteric material will be switched into the ~econd state (state B) if the optical intensity exceeds E1 but ls less than E2; and thirdly, the amphoteric material can be ~witched from the second state to the third state (~tate B to C) or from the ba~e state to the third state (states A to B to C~
when the optical intensity equals or exceeds E2. Therefore, by adjusting the intensity of the incident optical beam a spot on a Cu2[TCNQ:TCNQ(i~Pr)2] film can be switched into one of three ~tates. The switched state of the Cu2[TCNQ:TCNQ(i-Pr)~] material can be reversed by using optical or thermal means to heat the material. It will be noted that Equation 4 i6 rever~ible and that the charge transfer reaction can be reversed, or the ~memory erased~ using thermal radiation to reform the original charge transfer complex [i.e., returning ~he amphoteric material to its base state].
The Cu2ETCNQ:TCNQ(i-Pr)2~ amphoteric material has been shown only as an example. Similar organic amphoteric materials can be formed from other complex mixtures of two or more charge transfer salt~. In order to produce such an amphoteric organic charge transfer material two conditions must be met: (1) the two bistate charge transfer salts mu~t switch at different optical intensity thre~holds; and, ~2) the redox ~pecies generated by the electrochemical reaction must have different electronic optical infrared and/or Raman spectral properties.
Applicants have discovered a number of organic charge transfer compounds which will undergo bistate optical switching as above-described, in thepresence of energy from an optical field. Applicants have found that various TCNQ derivatives, when complexed with a metal donor, will form an orqanic charge transfer 0alt capable of optical memory and/or switching.
Examples of these TCNQ derivatives are ~hown in ~he following table:

TCNQ(OMe~ TCNQ I Me TCNQ(OMe)2 TCNQI
TCNQtOMe)(OEt~ TCNQ(OMe)(OCH~)2 TCNQ(OMEe)(O-i-Pr) TCNQ( CN ) 2 TCNQ~OMe)(0-i-Bu) TCNQ(Me~
TCNQ(O-i-C2H5l TCNQ(~t) TCNQ(OEt)(SMe) ~CNQ(i-Pr) TCNQ C1 TCNQ(i-Pr)2 TCNQ Br TCNQ Cl Me TCNQ Br Me Applicants have further found that i an organic electron acceptor contalning at least one cyanomethylene functional group is complexed with a donor moi~ty to form an organic salt, the organic salt will have memory and switching capabilities. Also Applicants have found that if an organic electron acceptor contains at least one quinolene unit is complexed with a donor moiety to form an organic salt, that organic ~alt will also have memory and ~witch capabilities. In ~pecific, if an organic salt is formed from the following organic electron acceptors, the organic fialt will be capable of optical memory and/or switching: tetracyanoquinodimethane (TCNQ), tetracyanonapthoquinodimethane (TNAP), tetracyanoethylene (TCNE), and 2, 3-dichloro-5,6-dicyano-1, 4-benzoquinone (DDQ), hexacyanobutadiene(~CBD), and 11, 11, 12, 1~-tetracyano-1.4 naphthoquinodimethane (benzo-TNAP), and 2,5-bis (dicyanomethylene)-2, 5-dihydrothiophene, and 2,5-bis z (dicyanomethylene)-2, 5-selenophene, and thiophene-(T)-TCNQ, and (selenophene-(Se)-TCNQ ~ and tetracyano-quinoquinazolinoquinazoline (TCQQ) and hexamethylcyanotrlmethylenecyclopropane (HMCTMCP) and 2,4-bis (dicyanomethylene)-1,3-dithietan (BDDT), and any of the TCNQ
derivatives shown in the above table~
Applicants have discovered that if the following metals are complexed with the above-referenced organic electron acceptor to form an organic salt, the organic salt will switch optically:
copper, ~ilver, lead, nickel, lithium, sodium, potassium, barium, chromium, molydenum, tungsten, cobalt, iron, antimony, cesium and magnesium. In addition, the following organic substances can also act as donors, and if complexed with an organic electron acceptor to form an organic ~alt, the organic salt will be eapable of optical memory and/or switching:
tetrathioethylenes, dithiodaminoethylenes, dithiodisalino ethyelenes, tetraminoethylenes, arenes, and aromatic hydrocarbons. It is to be understood that other organic transfer salts formed with organic electron acceptors having either cyanomethylene functional groups or quinolene units and other organic salts having similar characteristics, may be found which switchfrom the above-referenced first state to second state in the presence of optical radiation. The bistate optical switching compounds can be combined as taught herein to produce a multistate amphoteric organic charge transfer medium.
The switched states for such amphoteric organic charge transfer materialscan be distinguished because Raman modes of neutral and radical ion species are strongly affected by substitute groups attached to the quinoid structure. Optical properties associated with different redox species can be identified by a variety of different techniques. In ~eneral, 1~

~pectroscoplc means can be used to determine the particular state of a location on a multi~tate amphoteric char~e tran6fer medium. Both lnfrared ~pectro~copic means and Raman spectroscopic means can be used to identify the particular switched ~tate. Although Applicants' prefer to use Raman ~pectroscopic techniques, or ~imilar techniques which analyze a particular narrow band of la~er light reflected from the multistate amphoteric organic charge transfer medium, it is to be understood that any other well known spectroscopic or similar technique can be used which has the capability of identifying a change in oxidation ~tate of the organic electron acceptor moiety or change in the reduction state of the donor moiety (i.e., X-ray photoelectron spectroscopy (XPS), Raman or infrared spectroscvpic means can detect the change in oxidation state of the donor and/or the organic electron acceptor moiety).
In certain cases the redox species characteristic of a particular switch state can be identified by visual color changes in the material. The table in Figure 4 outlines some of the observed color changes in bi~tate material which car- be mixed to form multistate material. In addition, some of the organic acceptor molecules such as TCNQ(OMe)2, TCMQ
(o-i-Pr)(OMe) and TCNQ (i-Pr)2 exhibit a broad band fluorescence in the oxidized fi~ate but not in the reduced state. This fluorescence, ~hown in Figure 5, can be used to record the chanye in oxidation ~tate and to ~eparate the different redox species from one another for certain materials in this case TCNQ[(OMe)(O~i-Pr)J (e.g., the presence of fluorescence may indicate that a particular neutral redox species is present). Therefore, multistate amphoteric char~e transfer materials can be produced from two different bistate radical ion salts. Such multiswitching can be made from a variety of related radical ion acceptor molecules. Som~

l~f69~2 examples of ~uch acceptor molecul~ are listed above ~nd shown in Figure 6. The multi~witching effect can be ob6erved in these acceptor~ by mixing different molecules together or by changing the donor metal. For example, a multistate amphoteric organic charge transfer material made from a film composed of CuTCNQ and AgTCNQ will ffwitch at different applied optical field~. The optical field inten~ity at which a constituent bistate charge transfer salt switche~ i~ dependent upon the strength of the donor-acceptor bond.
It is also contemplated by the inventors that three or more bistate organic charge transfer sal~s can be combined as taught herein to form an amphoteric charge transfer material which will exhibit four or more ~witching states.

M~LTISTATE AMP~OT~RIC CHARGE TRANSFER CO~PLEX FORMED BY
CHE~ICALLY LINKING lfWO OR_ ORE ~ISTATE C~Ra~ AT~FER
HOLEC~LES
An alternative method for producing a multistate amphoteric charge transfer material i~ to chemically link variou~ acceptor molecules together through -f~igma and pi bonding ~ystems to produce a large molecule. The large molecule produced is amphoteric and can be switched optically into several states with each state identifiable by a unique set of redox species.
This method guarantees that the acceptor molecules will react with the metal donor equally to ~orm a molecular multi~witching system. Figure 7 shows several examples of two linked radical ion acceptor molecules. It will be noted that many known chemical linking chains can be u~ed other than those illustrated in Figure 7. The two chemicatly linking molecules shown in Figure 7, connect the TCNQ moiety with a TCNQ moiety having substitute R groups such as chlorine, bromine, fluorine, CH3, f`

OMe or other similar substituent groups. It will be noted that during the electrochemical switching reaction the covalent bonds 16~
between the linkin9 ch~in ~nd the TCNQ moiety and the llnking chain ~nd t~le ~CNQ derivative moiety do not break. It will also be noted that Raman spectro~copic mode6 for the redox ~pecies ~re atron~ly affected by ~uch ~ub~titute groups attached to the quinoid ~tructure -- thus ~llowing various redox species formed during the electrochemical reaction to be easily identified u~ing optical and ~pectroscopic techniques.
Equation (5j de~cribes~the multistate switching reaction for a (TCNQ)-CH2SCH~COCH2SCH2-(TNAP) amphoteric charge tran~fer molecule:

E

(5) nCu2 [(~CNQ )-R-(TNAP ~]

(State A) XCu~ XCu 1 (~CNQ ) -R- (~NAP ) ] - (n-x) Cu2 C (TCNQ- ) -R- (TNAP )]
(State B) 2 (x~y+z)Cu + (x-y)Cu ~(TCNQD)-R-(TNAp) ]

(y+z)[(TCNQ ) -R-(TNAP) ] + (n-y-z) Cu2[(TCNQ) -R-(TNAP) ]

(State C) where, R =c~2scH2cocH2sc~2 E2 > ~1 When the (TCNQ)-R ~TNAP) amphoteric charge transfer ~aterial, where R represents the -CH2SCH2COCH2SC~2- chemical linking chain, is illuminated by an optical beam having an intensity equal to or greater than El but less ~han E2I the material will switch from the base ~tate (state A) into the second state (~tate ~). As ~hown in Equation (5) the [(TCNQ)-R-~TNAP-)] and [(TcN~T)~R-lTNAp~)J redox ~pecies are pxe6ent in the second state. Optical and spectroscopic means, di8cussed earlier in this specification, can iden~ify the second sta~e by detecting the presence of the [(TCNQQ)-R-(TNAP )~ redox species. When the optical intensity is increased and is ~qual to or greater than E2 the material will be switched from the ~econd state to the third state (state B to C) or from the initial or base state to the third 6tate Istate A to B to C). AR shown in Equation (5) the [(~CNQ~)-R-(TNAP)], [[TCNQ~ (TNAP~3]and t(TCNQ)-R-(TN~P~)] redox species are present in the third ~tate. Optical or spectroscopic mean~l discussed earlier in this specification, can identify the third ~tate by detecting the pre~ence of the ~(TCNQ)-R-(TNAP)] redox species. It must again be noted that the covalent bonds joining the linking chain TN~P
to the TCNQ and ~M~ moieties are not broken even when the acceptor moiety i8 in the reduced htate, e.g.
[(TCNQ~-R-(TNAP)] redox species.
Although the [(TCNQ)-R-[TNAP)~ compound has been used to describe the amphoteric material formed by a chemically linking process, it is to be understood that other bistate organic charge transer salt can be joined by equivalent chemical chains to ~orm amphoteric molecules. The molecules diagrammed in Figure 7 as well as the bistate switching compounds mentioned earlier in this application can be chemically linked to form amphoteric compounds which will exhibit multistate optical switching. It is within the contemplation of the inventors to claim chemically-linked amphoteric material~ generated by linki,ng bistate organic transfer salts. The only limitation being that the bistate organic charge transfer salt~, which are linked to form the amphoteric material must: (1) switch from their base state to a switched state at different applied fields %~

at optical frequencie6: and, ~2) the redox Qpecies generated by the multistep redox reaction mU8~ have eatures easily identifiable by optical/~pectroscopic means.
It is also contemplated by the inventors that two or more bistate organic charge transfer ~alt molecules or two or more multistate molecular compounds can be chemically linked to form a large molecular complex which can be optically switched into four or more states.
It l,lst also be noted that Equation (5) repre~ent~ a reversible reaction and that thermal energy generated by optical or thermal means can return part or all of the amphoteric material to the base state. By this process, inormation 6tored on such an amphoteric charge transfer medium can be ~erasedn.
M~LTISTATE AMPIIOTERIC CHARGE TR~NSFER MATERIAL FORMED FROM A
DELOCALIZED AMPHOTERIC MOLEC~LAR SYSTEM
The aforementioned concepts can be utilized to synthesize and develop large delocalized molecular systems which exhibit ,-amphoteric redox properties in ~dditional to the optically induced charged transfer properties associated with the TCNQ

class of organic materials. Several important factors must be met to accomplish this end: I1) the synthesized molecule must underso an optically induced redox process and transfer electrons inter or intramolecular without rupturing electron pair igma bonds; (2) each radical partner in the molecular system must exhibit independent thermal ~tability; ~3) the optically induced electrochemical reaction which generates various redox species could ~e reYersible; and, ~4) the redox species must be readily identifiable llsing optical or other spectroscopic techniques. In essence, the sensitized molecules combine the multistate redox feature found in many known amphoteric molecules with the optical properties associated with the switching effect observed in copper and silver TCNQ type l6~
complexes. Examples of strongly delocalized radical ion acceptor molecule6 which exhibit the multiswitching effect are shown in Figure 8. Several o~ these amphoteric molecules (15,16) are derivatives of the TCNE radical ion with inserted alkene or aromatic groups (i.e., 2,3-dichloro-5,6 dicyano-1,4-benzoquinone and p-chloranil). Other molecules shown in Figure 8 (17, 18) are two-stage radical ions in which the end groups form part ~f a cyclic pi-system with exhibited aromatic characteristics in the oxidized ~tate (i.e., 2-dicyanomethylene-1,1,3,3, tetracyanopropanediide and hexacyanomethylenecyclopro-panediide). In addition, Fig. 8 illustrates one class of delocalized molecules l193 composed of tetracyanoarenoquinodimethane with an extended pi-~ystem; and, a compound (20) having alternate forms 1,3-squaric acid diamides; and, two compounds (21,22) composed of dicyanomethlyidene substituted with quinocyclo-propenes. In addition to acceptor type amphoteric molecules, amphoteric donor molecules complexed with radical ion electron acceptors will exhibit the optically induced multiswitching phenomena. Figure 9 shows several such amphoteric donor molecules including compound (23) benzotrithiophene; compound (24) heteroarene with bridgehead nitrogen atoms; compound (25) 4, 4'-bipyridium salts; compound (26) 4,4'-bithiopyran;
compound (27) 1,2-bis ~thioxanthene~9-ylidene) ethene; and, one of a class of compounds (28) 1,2-bi-l4H-thiopyran-4-ylidene) where X= substitute electron donors and/on electron acceptors.
The acceptor compounds can be complexed with various metals ~uch as copper, lead, nickel and silver. The multistate amphoteric charge transfer molecular compounds are grown as thin films or as single crystals which can be fabricated into various device geometries.

Equation (6) describes the multistate switching reaction in the material formed from Cu2~CloN6], an amphoteric charge transfer molecule:

(6) n CCu2 (CloN6) ] ~____~_ (State ~) ~

~ 2 xCu+ x[Cu (Cl0N6) ] ~ n-x(Cu2~C10 6 ~State B) (X+y+z) CU + X-y[cll (ClON6-)" ~ + ~Y+Z) (CloN6) + n-x-z[Cu2 (CloN6) ]

where E2~El When the Cu2iC1oN6~ material i5 illuminated by an optical beam haviny a field inten6ity equal to or greater than El but le~5 than E2, the amphoteric material will 6witch from the initial or base state ~State A) into the second state (State B). As ~hown in Equation (6); the CU2tC10~6] ~ and Cu 1C10N6]- redox ~pecies are present in the ~econd state. Optical and ~p~ctroscopic means discussed earlier in thi6 ~pecification, can identify the second state by detecting the pre~ence of the~e redox species. When the vptical inten~ity i~ increa~ed and is equal to or greater than E2 the material will be switch~d from the ~econd state to ~he third state ~5tate B to State C) or frvm the ~a~e ~tate to the third state ~State A to B to C). As shown in Equation ~6), the Cu2[C1oN6i 2~
Cu [C1oN6] ~Cu and CCloN6]2 redox species are pre~ent in the third state. Optical/spectroscopic means, di~cu~sed earlier in the specification, can identify the third state by detecting the presence of the Cu[C1oN632 redox species.
Although the Cu21CloN6] molecular 6tructure was shown in the ~bove example, it i6 understood ~hat other ~mphoteric molecular structures described earlier in Figure6 8 a6~2 ~nd 9, or Rimilax compound~, can form ~ynthesized molecular complexes which exhibit optical multi~tate switchinq. It is also contemplated that Ruch multistate ~yn~hetic molecules can be fabricated which have four or more switching states in a cordance with ~he present disclosure.
It must al60 be noted that Equa~ion (6) represents a reversible electron transfer reaction and thermal energy generated by optical or thermal means can xeturn all or part of the amphoteric material to the initial ~tate~ By this process, the memory medium formed from ~uch synthetic amphoteric molecule~ can be ~2rased~0 GENERALIZED SWITCHING CHARACTERISTICS OF MULTISTATE AMPHOTERIC
C~A~GE TRANSFER MATERIALS

_ _ The inventors have described three proces~es for forming a multistate amphoteric charge transfer medium. Generally, the amphoteric material is optically switched through a series of states by increasing the optical intensity. Figure 10 graphically illustrates the generalized optical switching characteristics. In the first or base state the organic switching medium is composed of redox species identified as ~B~in Figure 10. An optical "write~ beam is used to switch a spot on the material into a ~witched state tsuch spot referred as a "data storage spota3. If the optical intensity of the ~write~ beam exceeds an intensity threshold T1, but is less than threshold T2, the illuminated spot will jump to the second state. The second state can be identified by the ~ c"' 1' ~
appearance of a new redox ~4ci~ identified by A1 in Figure 10. (NOTE: The B redox species are ~till present at some reduced percentage and the A2 and A3 redox states are essen~ially absent.) As noted earlier, optical and .. . . . .
spectroscopic means, such Raman spectroscopy can identify the presence of the A1 redox speci~. If, however, the optical intensity exCeedB T2 but is 1eBS than T3, the material ~n the illuminated spot will jump into the third state. In the third state, the B, A1, and A~ ~pecie~ are present and can he identified by optical or spectroscopic means. Similarly, if the optical threshold exceeds T3, the material in the il luminated ~pot wil 1 be switched to the fourth state, where the B, A1, A2 and A3 redox species are pre~ent. By identifying the redox species present at a particular Rdata torage spot~, one can readily determine the ~witching ~tate of that ~pot.
Figure 11 i8 a truth table for ~uch a generalized amphoteric ~y~tem. The table shows that by identifying the presence o~
certain redox ~pecies, the state of the adata storage spota can be determined. For example, if the A4 redox species is detected by optical means, it indicates that the ~data ~torage spot~ is in state 4. If, the ~3 ~pecies i8 detected but not ~ignificant amounts of the A4 redox ~pecies, we are in the third state. If the A2 species i8 detected but not significant amounts of the A3 and A4 redox ~pecies, we are in the second state. If, however, the A2, A3 and A4 species are not significantly detected the ~data storage spot"
is in the the first or ba~e state.
The switching phenomenon observed in such amphoteric charge transfer materia~ can be either thre~hold switching or memory ~witching. For threshold ~witching the illuminated 6pot rapidly returns to the base state after the optical beam is removed.
For memory switching, the illuminated ~pot requires additional ene~rgy to return to the lower thermodynamically stable state after the beam is removed. In most cases, ambient thermal energy is insufficient to rapidly reverse the electrochemical reaction back to the lower state ~e.g., thermodynamically more stable state). The length of time memory can ~e retained depends on: (l) the particular ma~erial, ~2~ the diameter of the qwrite~ beam (3) ~he duraltion ancl intensity of the ~write~
beam; and (4) the thickness of ~mphoteric charge tran~fer film.
In several cases i~ has been demon~trated that the greater tne bondin~ nergy between the donor and acceptor ~pecies the larger the threshold level needed to switch from one ~tate to another and the greater likelihood that the switching action will be that of memory ~witching. Similarly, incident optical energy necessary to ~witch the amphoteric charge trancfer material from one state to anokher depends on ~everal factors including: (1) bonding energy; ~2) size of the illumination Wwrite~ beam; t3~
the duration of the optical ~write~ ~eam, and (4) the thickness or geometric arrangement of the amphoteric film or material. It will be noted that the frequency of the optical beam can be chosen from the ultraviolet, visible, and/or infrared regions of the electromagnetic ~pectxum. -~
Application of heat energy to a portion of the amphoteric material, which may be generated by an optical source, causes the amphoteric material to return to a more thermodynamically ~table state. If sufficient thermal energy i5 applied the amphoteric material will return to the hase state. In the preferred apparatus, described later, the inventors u5ed heat genexated by a CO2 laser to return a portion of the material to the base state.

MI~LTISTATE OPTICAL SWITCHING APPARATUS
The multistate amphoteric charge transfer material described in this application, can be used as the optical storage medium in various optical switching and storage apparatus. Figure 12 is a schematic diagram of an optical storage system using such a mul~tistate amphoteric charge transfer material as the optical storage medium. The amphoteric charge transfer m2terial 29 is deposited on or in a supporting base material 31. The amphoteric material can be grown on a metal donor base material 31, a~ described earlier in the specification, or other methods such as 6puttering can deposit the amphoteric material 29 on the base material 31. An optional transparent protective coating 33 may. be deposited on the surface of the amphoteric material film 29~ An optical ~write~ beam 35 i8 focused on a ~pecific spot 37 on the surface of the amphster~c material 29. (This ~pot i8 referred to as a ~data storage spot~ he optical Uwrite~ beam can be a high inten~ity light Aource or la~er source 8uch as an Argon or C02 la~er focused to generate a field on the film surface in the area of the "data storage Rpot~. The optical ~write~ beam has ~everal di~crete intensity levels, each intensity level causing the ~data ~torage ~pot~ to switch into a particular state.
Therefore, the intensity of the beam will cause the ~data storage spot" to ~witch states -- for example, in a three-state .
optical medium where the optical beam intensity is at the first threshold (T1) ~he ~data storage spot~ will switch from the base state to the second state; at intensity T2 the Wdata storage spot" will be switch~d to the thlrd state, and, at an intensity of T3 the "data storage spot~ will be switched into the fourth state. Ac mentioned previously, the optical intensity necessary to produce the above state changes depends on the choice of the amphotexic material, the film ~hickness or geometry and the area and intensity of the optical awriteU
beam.
For memory sy~tems, an optical "write" 35 can be directed by ~nown optical or electrical control mean~ to other ~data storage spot~ locations on the surface of the amphoteric charge transfer material 29 and can ~witch ~uch other locations from the base state to one of several switch ~tates. By controlling the beam intensity at a specific ~data storaye ~pot~ location, multiple bits of data can be stored at that location in the optical 6torage medium.
~ or example, with an amphoteric organic charge transfer material, having a three-stage electron transfer reaction, an optical "write~ beam can be used to switch the optical storage medium through the base state to one of three states depending on the intensity of the ~ptical field strength. Therefore, the "write" beam could be used to ~tore a three bit data code at each n data storage ~potN, If the memory apparatu~ were used in conjunction with a binary computer, the first or ba e state could be represented by ~01~, the ~econd switche~ state could be represented by a ~lOU; and, the third switched ~tate could b~
represented by a ~ . Alternatively, th~ memory apparatus could be used in connection with a base three computing system.
Once data has been 6tored on the storage medium, a spectro~copic means can be used to determine the particular switched state of the ~data 6torage epot~ being evaluated.
Figure 13 is a schematic of the spectroscopic means and shows ~data storage spot~ locaiizations 37 and 39, ~hich are two of a possible plurality of storage locations containing data. A
light source~ or ~readingW optical beam 41 i5 directed to illuminate one of the locations 37 with an intensity well below the first intensity thre~hold, 80 that ~he ~tate at location 28 .`
i~ no~ disturbed. The l~ght Rource 4 l~ for Raman spectroscopic analysis, could be a monochromatic sour~e and Applicants suggest the use of a laser ~ource. Reflected andtor emitted light 43 from the selected location on the film surface 37 is collec~ed and filtered by the optical band pass filter 45 allowing reflected light to pass through an optical means 47 for measuring the spectral intensity of each desired band. The optical means looks at the magnitude of particular spectral bands (Raman bands) which identify a particular redox species.

(It would be possible to have a plurality of filter/detector Ir combinations to measure the magnitude of reflected light in each band of interest. Alternatively, traditional Raman spectroscopic means could be utilized.) Based on the magnitude of the spectral intensity in each selected band, logic detection cixcuitry 48, of known design, determines the set of redox species present, which in turn uniquely defines the ~witched state of that r data storage 6pot~.
The ~reading~ optical beam 41 can be directed by well known optical means to each of the plurality of ~data storage ~pot~
locations (e.g., 37, 3B) on the ~urface of the amphoteric organic charge transfer material 29 to determine the state of eac~h particular location. That is to ~ay, for an amphoteric charge transfer material having three states, the spectroscopic means will determine the state of a particular Wdata storage ~pot~ and thereby determine the three-bit word ~tored at that ~data storage ~pot~.
Figure 14 is a schematic drawing show~ng the thermal erase means which is use~ to reverse the elec~rochemical charge transfer reaction and cause at least one of a plurality of ~data storage ~pot" locations on the surface of the amphoteric organic charge transfer material 29 to return to the base state. Figure 14 shows two alternative embodiments for the thermal erase means. The first embodiment uses thermal radiation from an op~ical beam 49 focused on the location 37 to generate sufficient heat to switch the area back to the base state.
Applicants have found that the CO2 laser, with an intensity below the first threshold, can be focused on location 37 for a time period long enough to generate sufficient thermal energy to switch the location back to the base state, ox more thermodynamically stable state. The optical heating beam~ can be directed by a ~ell kno~n optical means to erase other 3~

69~
locations on the amphoteric organic charge tran~fer material surface 29. An alternative embodiment uRe an electrical heating element 51, located below substrate 31, to generate sufficient thermal energy to ~exase" a portion of the amphoteric chaxge transfer material film 29.
In an alternative embodiment, ~he optical write ~eam 35, optical read beam 41, and the optical heating beam 49, can be qenerated by a 6in~1e laser source by varying the intensity and duration of the illuminating beam. It is within th~
contemplation of the Applicant~ that other well known means can be used to generate the desired optical ~write/read" and ~erase"
beams, and to direct such beams to the desired location on the amphoteric organic charge transfer material ~urface.
Obviously many modifications and variation~ of the present invention are possible in light of the above teachings. It is therefore to be understood that within the ~cope of the appended claims the invention may be practiced otherwise than as specifically described.

Claims (69)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An optically sensitive apparatus comprising a multistate optically sensitive organic charge transfer medium composed of at least two organic compounds, each of said organic compounds containing an electron donor moiety complexed with an organic electron acceptor moiety, wherein each of said at least two organic compounds has a different redox potential 80 as to switch from a first oxidation state to a second oxidation state in response to the application of electromagnetic energy at optical frequencies and at a field strength unique to each of said organic compounds, and wherein the oxidation state of each one of said organic compounds has an identifiably different optical spectrum.

2. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an organic electron acceptor moiety selected from the group consisting of tetracyanoquinodimethane (TCNQ), tetracyanonapthoquinodimethane (TNAP), tetracyanoethylene (TCNE), and 2, 3-dichloro-5,6-dicyano-1, 4-benzoquinone (DDQ), hexacyanobutadiene(HCBD), and 11, 11, 12, 12-tetracyano-1,4 naphthoquinodimethane (benzo TNAP ), and 2,5-bis (dicyanomethalene)-2, 5-dihydrothiophene, and 2,5-bis (dicyanomethylene)-2, 5-selenophene, and thiophene-(T)-TCNQ, and (selenophene-(Se)-TCNQ) and tetracyano-quinoquinazolinoquinazoline (TCQQ) and hexamethylcyanotrimethylenecyclopropane (HMCTMCP) and 2,4-bis (dicyanomethylene)-1,3-dithietan (BDDT), and any of the TCNQ
derivatives defined by the notation::

TCNQ(OMe) TCNQ I Me TCNQ(OMe)2 TCNQI
TCNQ(OMe)(OEt) TCNQ(OMe)(OCH3)2 TCNQ(OMEe)(O-i-Pr) TCNQ(CN)2 TCNQ(OMe)(0-i-Bu) TCNQ (Me) TCNQ (O-i-C2H5) TCNQ(Et) TCNQ(OEt)(SMe) TCNQ(i-Pr) TCNQ C1 TCNQ(i-Pr)2.
TCNQ Br TCNQ Cl Me TCNQ Br Me

3. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an electron acceptor moiety selected from the group consist of:

TCNQ (OMe) TCNQ (OMe)2 TCNQ(OMe)(OEt) TCNQ Br TCNQ Cl Me TCNQ Br Me TCNQ I Me TCNQ I
TCNQ (CN)2 TCNQ (Me) TCNQ (Et) TCNQ (i-Pr).

4. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an electron donor moiety which is selected from the group consists of copper, silver, lead, nickel, lithium, sodium, potassium, barium, chromium, molydenum, tungsten, cobalt, iron, antimony, cesium, magnesium and having chemical properties which permit formation of an organic salt when complexed with an organic electron acceptor.

5. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an electron donor moiety which is selected from the group consisting of tetrathioethylenes, dithiodiaminoethylenes, dithiodiseleno ethyelenes, tetraminoethylenes, , aromatic hydrocarbons, and aromatic heterocyclics having chemical properties which permit formation of organic salt when complexed with an electron acceptor moiety.

6. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an electron donor moiety which is selected from the group consisting of silver and copper.

7. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an organic electron acceptor moiety which is an organic material incorporating at least one cyanomethylene functional group and having the chemical properties which permit formation of an organic salt when complexed with an electron donor moiety.

8. The apparatus of claim 1, wherein a particular one of said organic compounds further comprises an organic electron acceptor moiety which is an organic material incorporating at least one quinolene unit and having the chemical properties which permit formation of an organic salt when complexed with an electron donor moiety.

9. The apparatus of claim 1,further comprising a source of electromagnetic energy at optical frequencies, said electromagnetic energy illuminating an area on said organic charge transfer medium, thereby causing at least one of said organic compounds in said illuminated area to undergo an electrochemical topactic redox reaction in response to said electromagnetic energy and switch from a first oxidation state to a second oxidation state.

10. The apparatus of claim 9, further comprising a means for varying the field strength of said source of electromagnetic energy at optical frequencies to a plurality of particular levels, each particular level unique to a particular one of said organic compounds for causing said organic electron acceptor moiety of a particular one of said organic compounds to switch from a first oxidation state to a second oxidation state.

11. The apparatus of claim 1, further comprising a spectroscopic means focused on a portion of said organic charge transfer medium, for determining the oxidation state of each of said at least two organic compounds.

12. The apparatus of claim 9, further comprising a source of thermal energy for initiating a reverse reaction in a section of said organic charge transfer medium for returning at least one of said organic compounds back from the second oxidation state to a first oxidation state.

13. The apparatus of claim 1, wherein said first oxidation state of each of said organic compounds contains the organic electron acceptor moiety in the radical ion state and wherein said second oxidation state of each of said organic compounds contains the organic electron acceptor moiety in both the radical ion and neutral states.

14. The apparatus of claim 13, further comprising a spectroscopic means for determining the presence of neutral and radical electron acceptor moiety ions for each of said organic compounds.

15. The apparatus of claim 1, wherein the electron acceptor moiety of each of said organic compounds is chemically linked, so as to form a single delocalized molecule.

16. An optically sensitive apparatus comprising a multistate optically sensitive organic charge transfer medium composed of at least one organic compound, wherein said organic compound contains an electron donor moiety complexed with an organic electron acceptor moiety and wherein said organic electron acceptor moiety has at least two regions having different amphoteric redox properties capable of independently changing oxidation state in response to the application of electromagnetic energy at optical frequencies and at a field strength value unique to each of said particular regions of said organic electron acceptor moiety, and wherein the particular oxidation state of each of said regions has an identifiably different optical spectrum.

17. The apparatus of claim 16, wherein said organic compound comprises an organic delocalized molecule, and wherein said organic electron acceptor moiety has at least two isolated regions, each isolated region capable of independently changing oxidation state in response to the application of electromagnetic energy at optical frequencies.

18. The apparatus of claim 16, wherein said organic electron acceptor moiety comprises at least two individual component electron acceptor moieties, each of said component electron acceptor moieties having a different redox potential and each of said component electron acceptor moieties joined together through covalent linkage.

19. The apparatus of claim 18, wherein each of said component electron acceptor moieties is material selected from the group consisting of: tetracyanoquinodimethane (TCNQ), tetracyanonapthoquinodimethane (TNAP), tetracyanoethylene (TCNE), and 2, 3-dichloro-5,6-dicyano-1, 4-benzoquinone (DDQ), hexacyanobutadiene(HCBD), and 11, 11, 12, 12-tetxacyano-1,4 naphthoquinodimethane (benzo TNAP), and 2,5-bis (dicyanomethylene)-2, 5-dihydrothiophene, and 2,5-bis (dicyanomethylene)-2, 5-selenophene, and thiophene-(T)-TCNQ, and (selenophene-(Se)-TCNQ) and tetracyano-quinoquinazolinoquinazoline (TCQQ) and hexamethylcyanotrimethylenecyclopropane (HMCTMCP) and 2,4-bis (dicyanomethylene)-1,3-dithietan (BDDT), and any of the TCNQ
derivatives defined by the notation::
TCNQ (OMe) TCNQ IMe TCNQ(OMe)2 TCNQI
TCNQ(OMe)(OEt) TCNQ(OMe)(OCH3)2 TCNQ(OMEe)()-i-Pr) TCNQ(CN)2 TCNQ(OMe)(0-i-Bu) TCNQ(Me) TCNQ(O-i-C2H5) TCNQ(Et) TCNQ(OEt)(SMe) TCNQ(i-Pr) TCNQ C1 TCNQ(i-Pr)2.
TCNQ Br TCNQ Cl Me TCNQ Br Me

20. The apparatus of claim 18, wherein each of said component electron acceptor moieties is a material selected from the group consisting of:

TCNQ (OMe) TCNQ (OMe)2 TCNQ(OMe)(OEt) TCNQ Br TCNQ C1 Me TCNQ Br Me TCNQ I Me TCNQ I

TCNQ (CN)2 TCNQ (Me) TCNQ (Et) TCNQ (i-Pr).

21. The apparatus of claim 18, wherein said electron donor moiety is a metal copper, silver, lead, nickel, lithium, sodium, potassium, barium, chromium, molydenum, tungsten, cobalt, iron, antimony, cesium, magnesium and having chemical properties which permit formation of an organic salt when complexed with an organic electron acceptor.

22. An optically sensitive apparatus comprising a multistate optically sensitive organic charge transfer medium composed of at least one organic compound, wherein said organic compound contains an organic electron donor moiety complexed with an electron acceptor moiety, wherein said organic electron donor moiety has at least two regions having different amphoteric redox properties capable of independently changing oxidation state in response to the application of electromagnetic energy at optical frequencies and at a field strength value unique to each of said particular regions of said organic electron donor moiety, and wherein the particular oxidation state of each of said regions has an identifiably different optical spectrum.

23. The apparatus of claim 22, wherein said organic electron donor moiety comprises at least two individual component electron donor moieties, each said component electron donor moieties having a different redox potential and each of said component electron donor moieties joined together through covalent linkage.

24. The apparatus of claim 23, wherein said electron donor moiety is an organic material selected from the group consisting of tetrathioethylenes, dithiodiaminoethylenes, dithiodiseleno ethyelenes, tetraminoethylenes, arenes, aromatic hydrocarbons, and aromatic heterocyclics having chemical properties which permit formation of organic salt when complexed with an electron acceptor moiety.

25. The apparatus of claim 18, wherein said electron donor moiety is a metal and said metal is selected from the group consisting of silver and copper.

26. The apparatus of claim 18, wherein each of said component electron acceptor moieties is an organic material incorporating at least one cyanomethylene functional group and having the chemical properties which permit formation of an organic salt when complexed with an electron donor moiety.

27. The apparatus of claim 18, wherein each of said component electron acceptor moieties is an organic material incorporating at least one quinolene unit and having the chemical properties which permit formation of an organic salt when complexed with an electron donor moiety.

28. The apparatus of claim 16, wherein said organic electron acceptor moiety is a derivative of the TCNE radical ion with inserted alkene groups.

29. The apparatus of claim 16, wherein said organic electron acceptor moiety is a derivative of the TCNE radical ion with inserted aromatic groups.

30. The apparatus of claim 16, wherein said organic electron acceptor moiety is 2,3-dichloro-5,6-dicyano-1,4-benzoquinone.

31. The apparatus of claim 16, wherein said organic electron acceptor moiety is p-chloranil.

32. The apparatus of claim 16, wherein said organic electron acceptor moiety is a two-stage radical ion in which the end groups form part of a cyclic pi-system with exhibited aromatic characteristics in the oxidized state.

33. The apparatus of claim 16, wherein said organic electron acceptor moiety is hexacyanotrimethylenecyclopropanediide.

34. The apparatus of claim 16, wherein said organic electron acceptor moiety is 2-dicyanomethylene-1,1,3,3, tetra-cyanopropanediide.

35. The apparatus of claim 16, wherein said organic electron acceptor moiety is composed of tetracyanoarenoquinodimethane with an extended pi-system.

36. The apparatus of claim 16, wherein said organic electron acceptor moiety is 1, 3 squaric acid diamides.

37. The apparatus of claim 16, wherein said organic electron acceptor moiety is composed of dicyanomethylidene substituted with quinocyclopropenes.

38. The apparatus of claim 22, wherein said electron donor moiety is a polycyclic compound having at least one region of conjugation and wherein at least one ring of said polycyclic compound contains a hetro-atom having at least one unshared pair of electrons.

39. The apparatus of claim 22, wherein said electron donor moiety is benzotrithiophene.

40. The apparatus of claim 22, wherein said electron donor moiety is a heteroarene with unabridged nitrogen atoms.

41. The apparatus of claim 22, wherein said electron donor moiety is a 4,4'-bipyridium salt.

42. The apparatus of claim 22, wherein said electron donor moiety is 4,4'bithiopyran.

43. The apparatus of claim 22, wherein said electron donor moiety is 1,2-bis (thioxanthene-9-ylidene) ethene.

44. The apparatus of claim 22, wherein said electron donor moiety is a compound defined by the notation:

wherein X= substitute electron donor and/or electron acceptor.

45. The apparatus of claim 16, further comprising a source of electromagnetic energy at optical frequencies, said electromagnetic energy illuminating an area on said organic charge transfer medium, thereby causing at least one of said regions of said electron acceptor moiety in said illuminated area to undergo an electrochemical topactic redox reaction in response to said electromagnetic energy and to thereby change oxidation state.

46. The apparatus of claim 29, further comprising a means for varying the field strength of said source of electromagnetic energy at optical frequencies to a plurality of particular levels, each particular level unique to one of said regions of said electron acceptor moiety for causing said particular region to switch from a first oxidation state to a second oxidation state.

47. The apparatus of claim 16, further comprising a spectroscopic means focused on a portion of said organic charge transfer medium, for determining the oxidation state of each of said regions of said electron acceptor moiety.

48. The apparatus of claim 45, further comprising a source of thermal energy for initiating a reverse reaction in a section of said organic charge transfer medium for returning at least one of said regions of said electron acceptor moiety back from the second oxidation state to the first oxidation state.

49. The apparatus of claim 1, wherein said change in oxidation state of each of said organic compounds causes an identifiable change to said electrical impedance of an illuminated area of said charge transfer medium.

50. The apparatus of claim 16, wherein said change in oxidation state of each of said regions of said electron acceptor moiety causes an identifiable change to the electrical potential of an illuminated area of said charge transfer medium.

51. The apparatus of claim 11, wherein the particular oxidation state of each of said organic compounds has a unique Raman absorption spectrum, and wherein said spectroscopic means utilizes such Raman absorption spectra to identify the set of oxidation species present in a portion of said charge transfer medium.

52. The apparatus of claim 47, wherein the oxidation state for each particular region of said electronic acceptor moiety has a unique Raman absorption spectrum, and wherein said spectroscopic means utilizes such Raman absorption spectra to identify the set of oxidation species present in a portion of said charge transfer medium.

53. The apparatus of claim 51 , wherein the particular set of oxidation species detectable by said spectroscopic means uniquely defines the state of said portion of charge transfer medium.

54. The apparatus of claim 53, further comprising:

a means for directing a source of electromagnetic energy at optical frequencies to a selected one of a plurality of data storage spots on said charge transfer medium, and, a means for varying the field strength of said source of electromagnetic energy at optical frequencies to a particular one of a plurality of levels, each one of said plurality of levels causes said data storage spot to switch to a particular state, each state being identifiable by a unique set of oxidation species.

55. The apparatus of claim 54, further comprising a means for directing the spectroscopic means to one of a plurality of data storage spots, and wherein said spectroscopic means identifies the set of oxidation species present in said particular data storage spot, thereby determining the state of said spot and identifying the data stored in said data storage spot.

56. The apparatus of claim 55, wherein said spectroscopic means further comprises:

an optical read beam for illuminating said particular data storage spot; and, an optical means for collecting light reflected from said particular data storage spot and for measuring the spectral intensity at a plurality of preselected spectral bands.

57. The apparatus of claim 56, wherein said optical means measures the spectral intensity at a plurality of preselected Raman bands.

58. The apparatus of claim 55, wherein said spectroscopic means detects fluorescence emission from said particular date storage spot.

59. The apparatus of claim 56, wherein said spectroscopic means further comprises a detection circuit means for determing the switched state of said particular date storage spot based on the pattern of spectral intensity in said preselected spectral bands.

60. The apparatus of claim 56, wherein said source of electromagnetic energy at optical frequences and said optical read beam are a single illuminating beam adjustable to a plurality of intensity levels.

61. A method for optically storing information, comprising the steps of:

directing an optical write beam to a particular spot on a multistate optically sensitive organic charge transfer film;
and, irradiating said particular spot at a selected one of a plurality of preset field strength values, so as to switch said particular spot into a particular one of a plurality of states.

62. The method of claim 61, further comprising the steps of:
illuminating a particular data spot on said multistate optically sensitive organic charge transfer film at an intensity below the lowest switching threshold of said material;

collecting light reflected from said particular data spot;

measuring the spectral intensity of said reflected light at predetermined spectral bands; and, assigning a switched state to said particular data spot based on the pattern of spectral intensity in said predetermined spectral bands.

63. The method of claim 62, wherein said predetermined spectral bands are Raman bands.

64. The method of claim 61 further comprising the step of:

applying thermal energy to a portion of said multistate optically sensitive organic charge transfer film to return said portion back to a more thermodynamically stable state.

65. The method of claim 64, wherein said thermal energy is provided by an optical beam.

66. The method of claim 64, wherein said thermal energy is provided by an electrical heating element.

67. An optically sensitive apparatus comprising a multi-state optically sensitive organic charge transfer medium composed of at least two organic compounds, each of said organic compounds containing an electron donor moiety complexed with an organic electron acceptor moiety, wherein each of said at least two organic compounds has a different redox potential so as to switch from a first oxidation state to a second oxidation state in response to the application of electromagnetic energy at optical frequencies at a field strength unique to each of said organic compounds, wherein the oxidation state of each one of said organic compounds has an identifiably different optical spectrum, and wherein a particular one of said organic compounds further comprises an organic electron donor moiety selected from the group consisting of: tetrathioethylenes, dithiodiaminoethylenes, dithiodiselenoethylenes and tetraminoethylenes.

68. An optically sensitive apparatus comprising a multistate optically sensitive organic charge transfer medium composed of at least two organic compounds, each of said organic compounds containing an electron donor moiety complexed with an organic electron acceptor moiety, wherein each of said at least two organic compounds has a different redox potential so as to switch from a first oxidation state to a second oxidation state in response to the application of electro-magnetic energy at optical frequencies at a field strength unique to each of said organic compounds, wherein the oxidation state of each one of said organic compounds has an identifiably different optical spectrum and further wherein the second oxidation state of one organic acceptor moiety exhibits fluorescence.

69. The apparatus of claim 68, wherein the organic acceptor moiety exhibiting fluorescence is one of: